1. Field of the Invention
The present invention relates to an AC motor, suitable for installation in an automobile, a motor truck, and so on.
2. Description of the Related Art
In the prior art, types of synchronous AC motor, and in particular types of brushless AC motor, are known which have stator windings formed as closely packed layers of conductors that are wound around the stator poles, for example as described in Japanese Patent Laid-open publication No. JP H6-261513 (see page 3, and FIGS. 1 to 3 thereof).
Such a configuration of conventional brushless motor disclosed in the Japanese Patent Laid-open publication No. H6-261513 is widely used at the present time in both industrial and domestic applications. However such a brushless motor has a complex construction, due to the need to form windings around each of the respective stator poles, with each of the windings being disposed in the interior of a stator slot. Hence, the manufacturing productivity is low. It is further difficult to produce such a type of brushless motor in a compact size, or to manufacture it at low cost.
In order to solve the above conventional problem, the inventor according to the present invention has invented an improved technique “A synchronous AC motor having stator windings formed as loop coils, and control apparatus for the AC motor” disclosed in the Japanese Patent Laid-open publication No. JP 2005-160285. This improved technique shows a synchronous AC motor, and in particular a brushless motor, having a simple configuration and ease of manufacture, which can be made compact in size, can operate with high efficiency, and has low manufacturing cost. The technique has further provided a control apparatus for such an AC motor. This synchronous AC motor has a rotor, a stator, and a plurality of loop-configuration stator windings. The rotor has a plurality of magnetic poles formed circumferentially, with N poles and S poles successively alternating. The stator has a plurality of stator poles formed around its inner circumference, arranged as N stator pole groups (where N is a plural integer) with each of adjacent pairs of the N stator pole groups mutually differing in circumferential position and axis position by an identical amount. The plurality of loop-configuration stator windings are formed circumferentially on the stator, with each loop-configuration stator winding are disposed immediately adjacent to a corresponding one of the N stator pole groups (with respect to the rotor axis direction).
Use of such loop-configuration stator windings is made possible by the fact that with a conventional form of stator winding, with each winding being wound a number of times around each of a plurality of stator poles in succession, those stator winding portions which are located at positions intermediate between adjacent poles produce magnetizing forces that mutually cancel, since respective currents of equal value and opposite direction flow through these portions of the stator windings. Hence, this is equivalent to a condition in which no current flows through these portions of stator windings, so that these can be omitted. Use of loop-configuration stator windings according to the improved technique has the advantages that the amount of copper required to form the stator windings can be substantially reduced, and in addition, increased output torque and increased efficiency can be achieved for the motor. Furthermore the manufacturing cost can be lowered, e.g., with manufacture being simplified since it is not necessary to coil the stator windings around the stator poles, and the motor can be made lighter in weight. Moreover, due to the fact that the aforementioned winding portions that are located between each pair of adjacent stator poles in a prior art type of synchronous AC motor are omitted, it would be possible to increase the number of stator poles of a synchronous AC motor according to the improved technique, by comparison with a prior art type of such motor.
Moreover, due to the fact that the locations of the stator poles can be distributed in a balanced manner, along both the rotor axis direction as well as around the inner circumference of the stator, as opposed to having a small number of stator poles that are located along a single circumferential path, further advantages are obtained. Specifically, the forces of magnetic attraction acting on the stator by the rotor poles are applied in a distributed manner, thereby reducing the tendency for the stator to become deformed by these forces. Hence, vibration and noise which results from such deformation can be reduced.
The inventor has directed his attention that the output torque of the AC motor increases and the torque ripple thereof reduces according to a shape of stator poles, the AC motor having an improved shape of the stator poles is made of more compact size because of eliminating stator coil ends, and it is possible to have a high degree of freedom in shape and thereby to reduce cogging torque and torque ripple because of having 3-dimensional magnetic path.